This invention relates to a defects analyzer for solid materials.
In 1880 a photoacoustic effect was discovered by Alexander Graham Bell and its application has recently been reconsidered, and a photoacoustic spectrometer (hereinafter referred to simply as "PAS") is known as an example of an analyzer of this sort. According to the prior art, analyzers of this sort are manufactured on the basis of the following principle. When light is irradiated upon a substance, the substance absorbs the light and becomes excited. The excitation energy goes through (1) Photochemical reaction, (2) light emission and (3) non-radiative transition, and then returns to the ground level. In this case, when going through the non-radiative transition of the above (3), there occurs a thermal change within the substance since there is no place of escape of the energy. If, in this case, the light is modulated in amplitude, such thermal change exhibits a periodic change dependent upon the modulation frequency and the gas sealed in the sample cell also undergoes a similar periodic pressure change resulting in the occurrence of an acoustic wave within the gas. This acoustic wave is detected by a microphone and its PA (photoacoustic) spectrum is observed.
Consequently, the PAS according to the foregoing prior art has the following drawbacks.
(1) Since a microphone is used, acoustic waves to be detected are limited to those of low frequencies of the order of 10 Hz to 2 kHz, which is quite insufficient to measure the relaxation time from the excited state in solid. PA1 (2) Because a microphone is used, it is necessary to avoid vibration as far as possible and a sample must be set within a sealed gas cell. Consequently, great difficulties are encountered in operation. PA1 (3) Because a microphone is used, there must be adopted the technique of detecting an acoustic wave occurring from the surface of a solid into a gas. When the difference in density between solid and gas is taken into account, this method is very inefficient. Consequently, this method requires a very strong light source. PA1 (4) Because a microphone is used, the apparatus cannot be used in vacuum, and consequently an electron ray or corpuscular ray is not employable as the source of excitation energy. PA1 (5) Since it is necessary to produce a thermal change induced by light on the surface of a sample, the light must be sure to be chopped or modulated in amplitude.
It is the object of this invention to provide a crystal defects analyzer including acousto-electric transducer means disposed in close adherence to a sample to be analyzed through the medium of a filter layer whereby the foregoing drawbacks associated with the prior art are eliminated and there are attained high response, high sensitivity, compact size, vibration resistance and superior operationality.